Nickel-base alloys



Un d Sta s a e- Q fiw Patented Nov. 14,, 1961 v 3,008,822 NICKEL-BASEALLOYS Walter K. Boyd and Merritt E. Langston, Columbus, Ohio, andThomasE. Johnson, Milwaukee, Wis; said Walter K..Boyd and Merritt E.Langston assignors to Battelle Memorial Institute, Columbus, Ohio, :1corporation of Ohio; said Johnson assignor to Stainless Foundry &Engineering, Inc., Milwaukee, Wis., a corporation of Wisconsin I NoDrawing. Filed July 30, 1959, Ser. No. 830,473

' r 2 Claims. (Cl. 75-171) 7 This invention relates to nickel-basealloys. More particularly, the invention relates to nickel-base alloyscomposed primarily of nickel, but including a substantial amount ofchromium and smaller amounts of other elements. These alloys exhibitremarkable resistance to corrosion. g I

Nickel alloys have been, and are presently, used in the chemicalprocessing industry for corrosion-resistant applications. In thisindustry, in handling chemicals and solutions of corrosive materials,such as acids, alkalis, and the like, particularly at elevatedtemperatures, it is highly desirable that equipment in contact with thecorrosive environments be of a material possessing a high resistance tocorrosion. For example, nickel alloys are used for equipment, such aspumps, impellers, shafts, cellophane hopper lips or blades, valves,pipes, bearings, pipe fitfingavessels, tanks, and the like in thisindustry. However, the nickel alloys presently employed in theseapplications have a limited range of practical utility. For example,nickel alloys suitable for use at either a low or a high concentrationof acid ordinarily are not satisfactory at an intermediate concentrationof acid. Likewise, nickel alloys suitable at low temperatures are nottoo satisfactory at high temperatures. 7 V g It is an object of theinvention to provide new nickelbase alloys exhibiting a remarkableresistance to corrosion. It is a further object to-provide newnickel-base alloys exhibiting superior corrosion-resistant propertiesover a broadrange of temperature and concentration of corrosive media,which alloys are of great value to the chemical processing industry. Itis still afurther object In accordance with theinvention, thenickelabase alloys consist essentially of 26 .to 30'pe'rcent chromium,

' included in the alloys.

7.5 to 9.0 percent molybdenum, 4 to 6.5 percent copper, and the balance-essentially nickel. Generally up to 1.6

percent manganese, up to 2.0 percent iron, up to 2.0

percent silicon, and up to 0.06 percent carbon, also are Titanium may beadded to these nickel-base alloys and may be present in residual amountsup to a maximum of 0.25 percent. Small or residual amounts of otherelements and/or concomitant impurities (i.e., sulfur, phosphorus, etc.)generallyfound in nickel alloys up to 0.15 percent also may be present.In the application and claims, unless expressly stated otherwise, allparts and percents are expressed as parts and percents by Weight.

The nickel-base alloys of the invention have constituent-s upon analysis(percent by weight) falling the following broad, preferred, and optimumranges:

Table I Amount, percent'by weight The broad range of compositions inTable I sets forth the alloys providing improved corrosion resistanceover broad ranges of temperature and corrosive material concentrationfor many corrosive materials. The preferred range of'compositions inTable I sets forth .the preferred alloys providing corrosion resistancesuperior to known alloys presently used in the chemical processingindustry.

to provide alloys, composed primarily of nickel, but ineluding asubstantial amount of chromium and smaller amounts of other elements,which alloys are characterized by exceptional corrosion resistance toconcentrated acid at elevated temperatures. It is another object toprovide alloys of the character described herein, which The optimumrange of compositions in Table I sets forth the alloys providing optimumcorrosion resistance to concentrated sulfuric acid at elevatedtemperatures.

The alloys of the invention may be prepared by present day meltprocedures for nickel alloys. One method of preparation is as follows:An induction furnace is charged with a suitable grade of commerciallypure nickel. Grades of nickel, such as nickel scrap, electrolyticnickel, powdered nickel briquettes, nickel powder, or nickel shot maybeused. After the furnace charged and the nickel brought to a moltenstate,the' molten nickel is preferably protected by a slag of any knowntype suitable for nickel alloys. Depending greatly on the particulargrade of nickel being used and its carbon content, a carbon boil may beused to adjust the carbon temperatures where present nickel alloys findlimited application because of the high corrosion-rates, of the priorart alloys. The nickel-base alloys of the invention also possess otherdesirable physical characteristics essential to their .being usedinequipment for'the chemicalprocessing industry. V I

For their greatest utility, the nickel-base alloys of the inventionusually are employed in the cast form. This cast form is capable ofbeing readily machined and welded. Additionally, these nickel-basealloys possess a degree of hot and cold workability that permits atleast a limited forgeability, rolling, swaging, and the like.

content of the alloy. Chromium and molybdenum in the required amountsare then added. When the mass is again molten, the requisite amount ofcopper is added. Preferably the constituents, which are added, are forpractical purposes in at least a commercially pure state, to avoidintroduction of unwanted constituents or too much of essentialconstituents. Preferably, to minimize chromium losses, a-si1itableconventional reducing agent is added to the slag. When the molten massreaches a desired pouring temperature, generally a temperature between2750 to 2950? F., at suitable scavenger ofthe desired type is added. Thescavenger may contain mam ganese, silicon, and*titanium,iandis capableof elimi. nating oxides and gases, and reducing the sulfur level,

. while bringing the manganese, silicon, 'andtitanium to within theconstituent amounts of the composition ranges of the alloys of theinvention. Then the molten mass is quickly cast or poured into suitableforms or molds;

As specific-examples of alloys of the invention,v which have beenprepared and which have been shown to provide the advantages of theinvention, the following compositions by analysis are illustrative:

1 Less than 0.1% titanium, less than 0.005% sulfur, less than 0.005%phosphorus, with the balance essentially nickel.

To evaluate corrosion resistance of the nickel-base alloys, cast andmachined samples of various alloys were immersed in aqueous solutions ofvarious acid concentrations at several temperatures. These alloy sampleswere supported on glass supports in the acid solutions. After each48-hour period of immersion, each sample was removed, rinsed withdistilled water, rinsed with acetone, and then oven-dried. Loss ofweight of a sample was converted to the calculated reduction inthickness which a large casting would undergo under similar conditionsin a one-year period. Data obtained are reported as the average ofreplicate samples for three 48-hour periods ofimmersion. Data arereported as corrosion rate in inches of penetration per year (I.P.Y.), awell-recognized manner of presenting and evaluating corrosion re- Thealloys of the invention upon exposure to sulfuric acid concentrations ofless than 65' percent 'and/or'tem peratures less than 90 C. exhibitlower corrosion rates (i.e. smaller losses in inches of penetration peryear) than obtained at the higher acid concentrations and highertemperatures, illustrated inTable HI.

The alloys of the inventiongalso exhibit remarkable corrosion resistanceto manyother corrosive media at both high and low concentrations andtemperatures. For example, alloy No. A of Table II in 25% boiling'm'tricacid had a loss of 0.010 I.P.Y. (inches of penetration ,per year). Acommercial nickel alloy, presently widely used in the chemicalprocessing industry, for comparison purposes had a corrosion rate of0.197 I.P.Y. in 25% boiling nitric acid. Equipment made from alloycompositionsof the invention has exhibited exceptional utility incorrosive media in the chemical processing industry. While the ultimateservice life for equipment made of alloy compositions of the inventionhas not been completely determined, to date the service life of thealloy compositions of the invention has been found to be at least equalto and in most instances superior to commercially available nickel alloycompositions. With the alloy compositions of the invention there hasbeenobtained a service life of three to four or more times that obtainedwith many conventionally used nickel alloys. a

For comparison purposes, Table IV presents typical results ofconventional nickel alloys .(alloysNo. 6.07 and N0. 593) subjected tothe same corrosive media test to whichthe alloys of the invention wereexposed. Table IV also presents a number of illustrative, experimentalalloys having amounts of constituents falling outside the constituentranges of them'ckl-base alloys of the invention with results of thesecorrosive media tests illustrating" that these alloys do not possessthesuperior corrosionre sistance .found in the alloys of the invention.

Table IV 2 Composition (percent) Loss inlnches of penetrationper-year'(I.P.Y.)at 90C.

Alloy No.

' Sulfuric Acid Concentration Or Mo Cu Mn Fe S1 0 N1 22. 30 5. 6. 22'1.25 0. 98 0. 92 0. 05 62.70 0. 063 0. 022 0. 01 2 22. 38 6.00 6. 56 '0.99 6.39 '0. 99 0. 25 56. 85 0; 096' 0.051 0. 020 22. ,3. 80 i 6.18 1.22 1. 45 0. 73 0. 05 balance 0.050 0.019 0. 012 22. 40 5. 00 '6. 20 l.26 1. 26 0. 72 0. 03 balance '0. 033' 0. 018 0.012 21. 78 5. 45 6; 25 1.22 1.70 1. 86 0. 05 balance. -0. 034 0. 013 0.008 22. M30 6. 20. 1.20 1. 20 0.05 0.05 balance 0. 031 0. 016 0. 009 22. 20 12.10 4. 28 1.28 1. 37 0.60 0. 05 58. 00 0.022 -0. 015' 0.008 22. 45 12. 10 6. 36 l.30 1.45 0:56 0. 05 55. 0. 031' 0. 014- 0. 008 22. 63 12. 10 7. 24 1.291.48 0.03 0. 05 54. 46 0.022 0. 014' 0. 010 21. 50 13.50 6. 76 1. 15 1.73 0.70 r 0. 05- 55. 50 '0. 029 05012 0.006

sistance of metals. A corrosion rate of 0.020 I.P.Y. generally isconsidered the maximum tolerable rate in industrial usage.

Table III represents results of some tests of alloys of this inventionupon being exposed to corrosive sulfuric acid media:

Table III Loss in inches of enetratlon per year (I.P.Y.? at 90 C.

One of the outstanding advantages provided .bythe alloys of the:invention is a significant superiority at intermediate ranges of acidconcentration at elevated temperatures over prior art alloys; Acomparison of the corrosion rates of the .priorart alloys (No. .607 andNo.

593) of Table IV with thecorrosion ratesof the alloys of the inventionof Table III illustrates this advantage. For example, prior art alloysNo. 607 and No. 593 (Table IV) had corrosion rates of 0.063 I.P.Y. and0.096 I.P.Y., respectively, in a 65% sulfuric acid concentration at C.In comparison therewith, alloy A (Table III) of-the invention had acorrosion rate of 0.015v I.P.Y.at the same conditions or asuperiorcorrosion rate for the alloy of the invention of about one-fourth toone-sixth that for conventionally employed prior art alloys.

From test data of the natureas reported in Table IV for experimentalalloys it has been found that chromium contents-of less than 26%generally provide corrosion rates inferiorto those exhibited by the:alloys of the invention whether the molybdenum contents are vabove orbelow or within the contents specified for the alloys of the invention.Nickel alloys having chromium contents larger than 30% are morediflicult to machine and weld than the alloys of the invention. Thesehigher chromium alloys also are more expensive. Any slight benefit incorrosion rates that may be realized from chromium contents in excess of30% does not offset the increased cost and other resultantdisadvantages. Generally it has been found that the chromium content mayrange from 26 to 30% with advantages and improvements of the inventionbeing obtainable. Within this broad range of chromium, a preferred rangeof 27.5 to 30% of chromium generally provides a corrosion resistancesuperior to known alloys at one or more acid concentrations, and anoptimum range of 28.5 to 29.5% chromium provides the optimum corrosionresistance to concentrated sulfuric acid at elevated temperatures. Italso has been found in nickel-base alloys of a standard chromium contentthat increasing the molybdenum content generally results in animprovement in corrosion properties. In the alloys of the inventionthese corrosion resisting benefits are at a maximum over a molybdenumcontent broad range of 7.5 to 9.0%. Molybdenum contents above and belowthis broad range provide no appreciable improvement in corrosionresistance. Within this broad range of 7.5 to 9.0% molybdenum; apreferred and superior corrosion resistance is obtained from 8.5 to 9.0%molybdenum, with this range of molybdenum also providing the optimumcorrosion resistance to concentrated sulfuric acid at elevatedtemperatures.

Similarly in nickel-base alloys of a standard chromium content it hasbeen found that the copper level may vary from 4 to 6.5% with theimproved corrosion benefits of the invention being obtainable. Copperlevels above and below this broad range of 4 to 6.5% generally showlittle or no improvement in corrosion resistance over known alloys.Somewhat narrower ranges of 5 to 6% and 5.25 to 5.75% of copper havebeen found to provide preferred and optimum benefits respectively. Inaddition to the principal elements of nickel, chromium, molybdenum, andcopper, the alloys of the invention may comprise other elements inlimited amounts. Some carbon, iron, silicon and other concomitantimpurities (i.e. sulfur, phosphorus, etc.) are residual elements andgenerally unavoidable, out are kept as low as economically practicalwithin good melting practice and should be within the ranges set forthin Table I if results of the invention are to be obtained. Generally,the lower the level of such elements in the alloys the better thecorrosion resistance, with larger amounts being deleterious and notdesirable to impart a beneficial corrosion resistance. Theinclusion inthe alloys of manganese and titanium within the limited amountsspecified in Table 1 has been found to be desirable from a metallurgicalstandpoint.

From the foregoing description and specific embodiments thereof, it isbelieved apparent that the invention may be embodied in other specificforms without departing from the true spirit, scope, and essentialcharacteristics of the invention. Hence, in the present invention it isintended to be limited only to the extent as set forth in the appendedclaims and it is intended to embrace within these claims allmodifications and variations as fall within the meaning and purview andrange of equivalency of these claims.

What is claimed is: I

1. An alloy characterized by exceptional corrosion resistance to highconcentration of acid at elevated temperatures, the alloy in percent byweight consisting essentially of:

Chromium 27.5-30 Molybdenum 8.5-9.0 Copper 5-6 Manganese 1.01.5 Iron Upto 1.5 Silicon 0.5-1.0 Carbon 0.04 up to 0.06 Titanium Up to 0.25 NickelBalance 2. An alloy characterized by exceptional corrosion resistance tohigh concentration of sulfuric acid at elevated temperatures, the alloyin percent by weight consisting essentially of:

References Citedin the file of this patent UNITED STATES PATENTS ParrOct. 27, 1914 Jackson et al. May 20, 1952

1. AN ALLOY CHARACTERIZED BY EXCEPTIONAL CORROSION RESISTANCE TO HIGHCONCENTRATION OF ACID AT ELEVATED TEMPERATURES, THE ALLOY IN PERCENT BYWEIGHT CONSISTING ESSENTIALLY OF: